Welcome to HCM
We understand your concerns
I went through your problem descriptions. Please donot worry about what has happened.
Sometimes such pinching or burning sensation do appears before urination. such condition arises out of low water intake. The minerals available in the urine do have the capacity to sediment. That sediments settle around the urinary outlet. If your penis head is not frequently cleaned, this could cause infection or inflammation.
The problem about sex might have happened due to the anxiety
about the pinching sensation. Drink plenty of water for two or three days and wash the penis head properly.
Hope this answers your query. Available for further clarification.